Airworthiness Directives; Boeing Model 747SP Series Airplanes

SUMMARY: This document proposes the supersedure of an existing

airworthiness directive (AD), applicable to certain Boeing Model 747SP

series airplanes, that currently requires repetitive inspections for

cracks in the web of the wing front spar over engine numbers 2 and 3,

and repair, if necessary. This action would require additional

inspections in an area beyond that specified in the existing AD. This

action also would provide for a new, optional terminating modification,

which, if accomplished, would constitute terminating action for the

repetitive inspections. This proposal is prompted by a report of

cracking in the web in an area outside the inspection zone specified in

the existing AD. A crack in the web that is not detected before it

extends outside the chord footprints can allow fuel leakage. The

actions specified by the proposed AD are intended to prevent fuel

leakage onto an engine and a resultant fire due to cracking in the web

of the wing front spar.

DATES: Comments must be received by December 24, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-103,

Attention: Rules Docket No. 94-NM-120-AD, 1601 Lind Avenue, SW.,

Renton, Washington 98055-4056. Comments may be inspected at this

location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except

Federal holidays.

The service information referenced in the proposed rule may be

obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,

Washington 98124-2207. This information may be examined at the FAA,

Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton,

Washington.

FOR FURTHER INFORMATION CONTACT: Tim Backman, Aerospace Engineer,

Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle

Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,

Washington 98055-4056; telephone (206) 227-2776; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the

proposed rule by submitting such written data, views, or arguments as

they may desire. Communications shall identify the Rules Docket number

and be submitted in triplicate to the address specified above. All

communications received on or before the closing date for comments,

specified above, will be considered before taking action on the

proposed rule. The proposals contained in this notice may be changed in

light of the comments received.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the proposed rule. All

comments submitted will be available, both before and after the closing

date for comments, in the Rules Docket for examination by interested

persons. A report summarizing each FAA-public contact concerned with

the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit a self-addressed,

stamped postcard on which the following statement is made: ``Comments

to Docket Number 94-NM-120-AD.'' The postcard will be date stamped and

returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request

to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules

Docket No.94-NM-120-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

On August 6, 1990, the FAA issued AD 90-17-18, amendment 39-6702(55

FR 33279, August 15, 1990), applicable to certain Boeing Model 747SP

series airplanes, to require inspections for cracks in the web of the

wing front spar between front spar station (FSS) 636 and FSS 675 over

engine numbers 2 and 3, and repair, if necessary. That AD also provides

for an optional modification, which, if accomplished, constitutes

terminating action for the required inspections. That action was

prompted by a report of a 26-inch crack on the front spar web. The

requirements of that AD are intended to prevent fuel leakage onto an

engine and a resultant fire.

Since the issuance of that AD, the FAA received a report of

cracking in the web of the wing front spar in an area outside the

inspection zone specified in AD 90-17-18 on a Model 747SP series

airplane that had been inspected previously in accordance with that AD.

The report involved a 31-inch fatigue crack between front spar station

(FSS) 628 and FSS 659. The crack was initiated by sonic fatigue. In

addition, fuel was leaking adjacent to the number 3 engine. The FAA

also received a report of a 24-inch fatigue crack between FSS 646 and

FSS 670 on another Model 747SP series airplane. A crack in the web that

is not detected before it extends outside the chord footprints can

allow fuel leakage. Fatigue cracking on the web of the wing front spar,

if not detected and corrected in a timely manner, can result in fuel

leakage onto an engine and a resultant fire.

Based on these findings, the FAA has determined that additional

actions are necessary on airplanes that were inspected or modified in

accordance with AD 90-17-18. The FAA finds that an ultrasonic

inspection must be performed in an area that extends beyond that

specified in the existing AD. In addition, a high frequency eddy

current inspection of an area of the web one inch below the upper chord

and one inch above the lower chord footprints between FSS 628 and FSS

675 must be performed. Additionally, the FAA finds that these

inspections must be performed on airplanes on which the ``terminating

modification,'' which was provided in AD 90-17-18, was previously

installed.

The FAA has reviewed and approved Boeing Alert Service Bulletin

747-57A2259, Revision 2, dated June 9, 1994, which describes procedures

for additional inspections of an expanded inspection zone. This revised

alert service bulletin describes the following repetitive inspections

to detect cracks in the web between FSS 628 and FSS 675:

1. Ultrasonic inspections of the web under the upper and lower

chord footprints;

2. High frequency eddy current inspections of the web in an area

one inch below the upper chord and one inch above the lower chord

footprints; and

3. Detailed visual inspections of the forward face of the web of

the wing front spar at fastener locations in the web-to-stiffeners and

web-to-rib posts.

The alert service bulletin also describes procedures for

accomplishment of an optional terminating modification. That

modification involves removing a section of the web of the wing front

spar between FSS 623 and FSS 670 inboard of the inboard engine,

splicing in a new thicker web section, and adding a new stiffener

outboard of the web splice. If this modification is accomplished, the

repetitive inspections of the web, as described in the alert service

bulletin, are no longer necessary.

Since an unsafe condition has been identified that is likely to

exist or develop on other products of this same type design, the

proposed AD would supersede AD 90-17-18 to require various repetitive

inspections to detect cracks in the web of the wing front spar in an

area beyond that specified in the existing AD, and modification, if

cracking is found. Installation of the modification would constitute

terminating action for the repetitive inspections. The actions would be

required to be accomplished in accordance with the alert service

bulletin described previously.

Operators should note that this NPRM would supersede the existing

AD with new, additional inspections and a new terminating modification.

Airplanes on which the previous ``terminating'' modification provided

for in AD 90-17-18 had been installed would be required to be inspected

in accordance with the new inspections proposed in this notice.

Installation of the new terminating modification, specified in

paragraph (e) of this notice, would constitute terminating action for

the requirements of the AD.

The manufacturer has advised that it is currently developing a

modification program for the engine struts on these airplanes that will

positively address the fatigue cracking condition and other items

associated with the engine struts. Once this modification program is

developed and approved, the FAA may consider additional rulemaking.

There are approximately 35 Model 747SP series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 11

airplanes of U.S. registry would be affected by this proposed AD.

The FAA estimates that it would take approximately 22 work hours

per airplane to accomplish the proposed inspections (between FSS 628

and FSS 675) specified in this AD, and that the average labor rate is

$55 per work hour. Based on these figures, the total cost impact of the

proposed AD on U.S. operators is estimated to be $13,310, or $1,210 per

airplane.

The total cost impact figure discussed above is based on

assumptions that no operator has yet accomplished any of the proposed

requirements of this AD action, and that no operator would accomplish

those actions in the future if this AD were not adopted.

Should an operator elect to accomplish the terminating modification

that would be provided by this AD action, it would take approximately

644 work hours to accomplish it, at an average labor rate of $55 per

work hour. The cost of required parts would be $21,800. Based on these

figures, the total cost impact of the terminating modification would be

$57,220 per airplane.

The regulations proposed herein would not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of power and

responsibilities among the various levels of government. Therefore, in

accordance with Executive Order 12612, it is determined that this

proposal would not have sufficient federalism implications to warrant

the preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this proposed

regulation (1) is not a ``significant regulatory action'' under

Executive Order 12866; (2) is not a ``significant rule'' under the DOT

Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);

and (3) if promulgated, will not have a significant economic impact,

positive or negative, on a substantial number of small entities under

the criteria of the Regulatory Flexibility Act. A copy of the draft

regulatory evaluation prepared for this action is contained in the

Rules Docket. A copy of it may be obtained by contacting the Rules

Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration proposes to amend

part 39 of the Federal Aviation Regulations (14 CFR part 39) as

follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by removing amendment 39-6702 (55 FR

33279, August 15, 1990), and by adding a new airworthiness directive

(AD), to read as follows:

Boeing: Docket 94-NM-120-AD. Supersedes AD 90-17-18, Amendment 39-

6702.

Applicability: Model 747SP series airplanes; variable numbers

RG001 through RG142 inclusive, and RG171 through RG222 inclusive;

certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent fuel leakage onto an engine and a resultant fire,

accomplish the following:

(a) For airplanes on which the ``terminating modification''

[between front spar station (FSS) 640 and FSS 670] specified in

Boeing Alert Service Bulletin 747-57A2259, dated February 15, 1990;

or Revision 1, dated September 6, 1990; has not been accomplished:

Within the next six months after September 21, 1990 (the effective

date of AD 90-17-18, amendment 39-6702), perform a visual and an

ultrasonic inspection of the front spar web between front spar

station (FSS) 636 and FSS 675 in accordance with Boeing Alert

Service Bulletin 747-57A2259, dated February 15, 1990, or Revision

1, dated September 6, 1990. If no crack is found, repeat these

inspections at intervals not to exceed 1,000 landings until the

inspections required by paragraph (b) of this AD are accomplished.

(b) For airplanes on which the ``terminating modification''

[between front spar station (FSS) 640 and FSS 670] specified in

Boeing Alert Service Bulletin 747-57A2259, dated February 15, 1990;

or Revision 1, dated September 6, 1990; has not been accomplished:

Prior to the accumulation of 4,000 total landings on the airplane,

or within 1,000 landings after the effective date of this AD,

whichever occurs later, perform the inspections specified in

paragraphs (b)(1), (b)(2), and (b)(3) of this AD to detect cracks in

the web between FSS 628 and FSS 675, in accordance with Boeing Alert

Service Bulletin 747-57A2259, Revision 2, dated June 9, 1994.

Accomplishment of these inspections terminates the repetitive

inspection requirement of paragraph (a) of this AD. If no crack is

found, repeat these inspections thereafter at intervals not to

exceed 1,000 landings.

(1) Perform an ultrasonic inspection in the web under the upper

and lower chord footprints; and

(2) Perform a high frequency eddy current inspection in the web

in an area one inch below the upper chord and one inch above the

lower chord footprints; and

(3) Perform a detailed visual inspection in the forward face of

the web of the wing front spar at fastener locations in the web-to-

stiffeners and web-to-rib posts.

(c) For airplanes on which the ``terminating modification''

specified in Boeing Alert Service Bulletin 747-57A2259, dated

February 15, 1990; or Revision 1, dated September 6, 1990; has been

accomplished: Prior to the accumulation of 4,000 total landings on

the airplane, or within 6 months after the effective date of this

AD, whichever occurs later, perform the inspections specified in

paragraphs (c)(1), (c)(2), and (c)(3) of this AD to detect cracks in

the web between FSS 628 and FSS 636, in accordance with Boeing Alert

Service Bulletin 747-57A2259, Revision 2, dated June 9, 1994. If no

crack is found, repeat these inspections thereafter at intervals not

to exceed 1,000 landings.

(1) Perform an ultrasonic inspection of the web under the upper

and lower chord footprints; and

(2) Perform a high frequency eddy current inspection of the web

in an area one inch below the upper chord and one inch above the

lower chord footprints; and

(3) Perform a detailed visual inspection of the forward face of

the web of the wing front spar at fastener locations in the web-to-

stiffeners and web-to-rib posts.

(d) If any crack is found during any inspection required by this

AD, prior to further flight, accomplish a terminating modification

(between FSS 623 and FSS 670) in accordance with Boeing Alert

Service Bulletin 747-57A2259, Revision 2, dated June 9, 1994; or in

accordance with a method approved by the Manager, Seattle Aircraft

Certification Office (ACO), FAA, Transport Airplane Directorate.

(e) Installation of a terminating modification (between FSS 623

and FSS 670) in accordance with Boeing Alert Service Bulletin 747-

57A2259, Revision 2, dated June 9, 1994; or in accordance with a

method approved by the Manager, Seattle ACO; constitutes terminating

action for the requirements of this AD.

(f) An alternative method of compliance or adjustment of the

compliance time that provides an acceptable level of safety may be

used if approved by the Manager, Seattle ACO. Operators shall submit

their requests through an appropriate FAA Principal Maintenance

Inspector, who may add comments and then send it to the Manager,

Seattle ACO.

Note: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Seattle ACO.

(g) Special flight permits may be issued in accordance with

sections 21.197 and 21.199 of the Federal Aviation Regulations (14

CFR 21.197 and 21.199) to operate the airplane to a location where

the requirements of this AD can be accomplished.

Issued in Renton, Washington, on October 24, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-26716 Filed 10-27-94; 8:45 am]

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